Hydrocarbon treatment

ABSTRACT

The average degree of branching of a branched olefin feedstock is reduced by skeletal isomerization in contact with a molecular sieve.

This application is a 371 filing based on international applicationPCT/EP94/01937, filed Jun. 14, 1994, which in turn is based on GBapplication 9312245.5 filed Jun. 14, 1993.

This invention relates to the treatment of hydrocarbons, especiallybranched aliphatic hydrocarbons, and more especially olefinichydrocarbons, to effect isomerization of the hydrocarbon skeleton.

Olefinic hydrocarbons are employed as starting materials in thehydroformylation, or oxo, process, for the eventual manufacture ofnumerous valuable products, e.g., alcohols, esters and ethers derivedtherefrom, aldehydes, and acids. In many of those end uses, linear orlightly branched hydrocarbon chains have advantages compared with moreheavily branched chains.

In the oxo process itself, moreover, olefins with heavily branchedchains are less reactive than those with linear or lightly branchedstructures and, for a given degree of branching, certain isomers areless reactive than others.

Olefinic feedstocks, especially in the C₄ to C₂₀, and more particularlyin the C₆ to C₁₅ range, are frequently produced by oligomerization oflower molecular weight original starting materials, a process that,because of rearrangements that take place during the reaction, mayproduce an undesirably high proportion of multiply branched olefins,even if the original materials are linear. Also, the locations of thebranches, at sites close to each other on the hydrocarbon chain, or inthe central region of the chain, or both, resulting from theoligomerization further reduce the reactivity of the molecules in theoxo reaction.

There are other areas in which a less highly branched hydrocarbon hasadvantages; these include the alkylation of aromatic hydrocarbons byreaction with olefins in the manufacture of surfactants and polyolefinstabilizers.

There is accordingly a need to provide a method to reduce the degree ofbranching of a hydrocarbon material.

It has now been found that contacting a branched olefinic hydrocarbonmaterial with a catalyst in the form of a molecular sieve having a10-membered ring pore structure reduces the degree of branching of thematerial.

This finding is surprising since more highly branched isomers arethermodynamically more stable than less highly branched isomers. Thefinding is also surprising in view of the teachings of EP-B-247802 thata linear olefin may be isomerized to a branched olefin by contacting itwith a zeolite having such a structure, for example ZSM-23, examplesbeing given of isomerization of n-butene to isobutene.

U.S. Pat. No. 5,157,194 obtains similar results when employingmicrocrystalline ZSM-22, another 10-numbered ring zeolite, reportinghigh yields of isobutene from an n-butene feed.

In WO 91/18851, there is disclosed a process for interconversion,including isomerization, of unsaturated compounds, e.g., n-olefinscontaining 3 to 9 carbon atoms, using a catalyst comprising a molecularsieve ion-exchanged with a cation to provide a Lewis acid site. Suitablemolecular sieves include silica/alunina phosphates (SAPO) and zeolites.Favored conditions for isomerization include a temperature in the range250° to 500° C., especially 375° to 475° C., and a pressure of 0.08 to0.12 MPa, especially about atmospheric, n-butene readily isomerizing toiso-butene.

EP-A-523838 describes a similar process of isomerizing linear alkenes tobranched alkenes, while WO 93/03118 describes a process in which analkene feed is contacted with two catalysts sequentially for increasingthe branched alkene content.

The present invention provides a method of reducing the degree ofbranching of a branched olefinic feedstock, which comprises contactingit under conditions facilitating skeletal isomerization with a molecularsieve having a 10-membered ring pore structure.

The invention is applicable to all branched olefinic species, but isespecially applicable to olefins having from 4 to 20 carbon atoms, moreespecially to olefins having from 7 to 16 carbon atoms, and particularlyalkenes having from 7 to 12 carbon atoms. The feedstock to the reactionmay be a single species, a mixture of two or more alkene isomers havingthe same number of carbon atoms, or a mixture of two or more alkeneshaving a range of carbon atoms, for example a C₇ to C₁₂ mixture.

The invention is especially applicable to mixtures of olefinic specieshaving a degree of branching in excess of 1.80, especially in excess of1.95, more especially mixtures of nonenes having such a degree ofbranching. The degree of branching (D) of a mixture of olefins havingdifferent numbers of branches is defined as follows: ##EQU1## where x isthe molar proportion of unbranched species; y is the molar proportion ofspecies having m branches z is the molar proportion of species having nbranches, etc.

As examples of molecular sieves having a 10-membered ring pore there maybe mentioned the 10-membered ring representatives of thoaluminosilicates, aluminophosphates (AlPO), silicoaluminophosphates(SAPO) metalloaluminophosphates (MeAPO), andmetalloalluminophosphosilicates (MeAPSO). More especially, however,there may be mentioned 10-membered ring zeolites, e.g., ZSM-5, ZSM-22,ZSM-23, ZSM-48 and ISI-1 and KZ-2. The zeolites are conveniently used intheir acidic (H¹) form, either in the dehydrated or the partiallyhydrated state. The degree of hydration may be controlled by the zeolitecalcination conditions when removing the organic template (structuredirecting agent) if used in the manufacture of the zeolite or byhydration of the feed.

Calcination of the zeolite, if necessary because of the presence of atemplate, may be effected before use, either in an inert or oxidizingatmosphere, conveniently at temperatures within the range of from 350°to 550° C.

The catalyst may be in powder, granule or other shaped form, e.g., anextrudate produced in admixture with a suitable binder. The catalyst maybe readily regenerated, for example by a coke burn in air at atemperature of from 350° to 700° C., advantageously 400° to 5500° C., orby steam treatment, advantageously at 350 ° to 550° C.

A wide range of conditions is available for the isomerization reaction.Isomerization may advantageously be effected at a temperature within therange of from 50° to 350° C., preferably from 150° C. to 250° C. Anadvantageous pressure for the reaction is within the range of fromatmospheric to 10 MPa, preferably from atmospheric to 7.5 MPa. Thereaction may be carried out with the feedstock, reaction mixture andproduct in the gas, liquid, gas/liquid, or dense phase, depending on thetemperature and pressure used. The feedstock may consist essentially ofthe olefin reactant or it may comprise the olefin in admixture with aninert diluent or solvent, for example an alkane, as carrier.

The reaction may be carried out as a batch process, for example in anautoclaver or as a continuous process. In a continuous process, the WHSVof active feedstock is advantageously within the range of from 0.25 to 5w/wh, preferably from 1 to 2 w/wh.

In addition to reducing the average degree of branching of a mixedolefin feed, the process of the present invention also changes thelocation of the branch or branches in the olefin feedstock. The effectof this change is generally to increase the number of carbon atomsbetween branches, resulting in a product in which the branches arefurther apart and further away from the centre of the molecule. Ofcourse, in an olefin feedstock with a mixture of numbers and locationsof branches, it is not possible to identify the reactions individually,but overall the observation is as indicated above.

Using a mixed nonene feed, for example, the result may be summarized inthat in addition to reducing the proportion of dimethyl heptenes andincreasing that of methyl octenes, the proportion of3,4-dimethylheptenes decreases while that of 2,5-dimethylheptenes isincreased.

The isomerization reaction may be used alone or in combination withother reactions, either simultaneously or sequentially.

The present invention accordingly also provides a process in which anolefin or a non-olefinic starting material is converted into a branchedolefin, the resulting olefin is contacted under conditions facilitatingisomerization with a molecular sieve having a 10-membered ring porestructure, and, if desired or required, the isomerized olefin product isconverted into a different olefinic or non-olefinic species.

The invention also provides a process in which a branched olefin iscontacted under conditions facilitating isomerization with a molecularsieve having a 10-membered ring pore structure, and the isomerizedolefin product is converted into a different olefinic or a non-olefinicspecies, the branched olefin having been formed, if desired or required,from a non-olefinic or an olefinic species different from thatisomerized.

As an example of a process in which the starting material or finalproduct is non-olefinic, there may be mentioned the process mentionedabove in which the isomerized olefin product is subjected tohydroformylation.

As an example of a reaction sequence in which the starting material is adifferent olefinic species from that isomerized, there may be mentionedthat in which a low molecular weight olefin, for example, propene orbutene, is oligomerized to a higher molecular weight olefin, e.g.,octene, nonene or dodecene, and the higher molecular weight olefinisomerized as described above, the isomerized olefin then optionallybeing used as a hydroformylation feed or further oligomerized.

Such a sequence may be carried out by oligomerization of a light olefinfeed employing, for example, solid phosphoric acid, H-ZSM-5, acidicsilica, alumina or mixed silica/alumina, or a transition metal-basedoligomerization catalyst, as catalyst to give an oligomer mixture whichhas a high degree of branching, then skeletally isomerizing the mixtureby the process of the invention, if desired fractionating the oligomermixture beforehand. The product may be further oligomerized or used asfeed to hydroformylation.

The oligomerization and the subsequent isomerization may be carried outin different reactors, which is preferred isomerization is not alwaysrequired. This may be the case where the initial oligomerizationsometimes does and sometimes does not give rise to an oligomer mixtureor a downstream product according to an existing specification; theoligomer may be analyzed and the isomerization reactor brought on streamwhen necessary.

When, in contrast, isomerization is always required then, since thereaction conditions for oligomerization and isomerization aresubstantially the same, the oligomerization and isomerization catalystmay be placed in the same reactor either in series or in admixture.Mixtures of catalysts in the same bed are advantageously mixtures of twozeolite catalysts, e.g., ZSM-5 and ZSM-22.

As well as or, preferably, instead of isomerizing the oligomer olefinfeed to a reactor, e.g., a hydroformylation reactor, isomerization maybe carried out on unreacted olefin separated from the reaction productleaving the reactor, and recycled to the reactor. As indicated above,heavily branched olefins are less reactive in the oxo process than areless lightly branched isomers.

Since not all the olefin in the feedstock is converted to oxygenatedproduct in normal commercial operation of the oxo process, unreactedstarting materials are separated from the oxygenated product andrecycled. This eventually results in a serious loss of efficiency as theless reactive species build up in the recycled material as the reactionproceeds.

By employing the skeletal isomerization process of the present inventionon the unreacted olefins, these may be converted into more reactivespecies before recycling. The invention accordingly more especiallyprovides a process for hydroformylating an olefin feedstock in whichafter hydroformylation, unreacted olefin is separated from reactionproduct, contacted under isomerization conditions with a molecular sievehaving a 10-membered ring pore structure, and returned to thehydroformylation reaction.

This process has the advantage that it enables the hydroformylation tobe carried out at a lower conversion rate, thereby reducing by-products,e.g., heavy species and paraffins, and facilitates lower oxo catalystconsumption. Additionally, the average reactivity of the olefin feed tothe reactor is increased more efficiently if only unreacted olefin issubjected to the isomerization reaction since this will have a higherdegree of branching than the initial feed.

The following Examples illustrate the invention:

EXAMPLE 1

In this example, a dilute branched nonene feed is used as feedstock in acontinuous process. The conditions, resulting in a dense phase feed,were as follows:

    ______________________________________    Feed            3% by weight nonene fraction in                    propane    Catalyst        H-ZSM-22    Space Velocity  1.6 g/gh. (based on nonene                    content)    Temperature     200° C.    Pressure        7 MPa    Reactor         Continuous flow, fixed bed    Duration        5 hours    Reactive feed   C.sub.8.sup.-                            0.8%    Composition     C.sub.9.sup.+ C.sub.10                            97.6%    by weight       C.sub.11.sup.+                            1.6%    ______________________________________

Table 1 below shows the composition, in terms of branching of the nonenefraction, of the feed and of the product as collected over various timeperiods. All such analyses are carried out by gas chromatography afteron-line hydrogenation.

                  TABLE 1    ______________________________________    ISOMERS %    Isomers   LINEAR     1-Br   2-Br   3-Br D    ______________________________________    FEED      1.22       8.81   75.96  14.01                                            2.03    PRODUCT:    0.6 to 1.1 h              0.00       26.54  62.60  10.86                                            1.84    2.2 to 2.6 h              1.30       26.57  59.35  12.79                                            1.84    4.3 to 4.7 h              0.68       27.23  60.88  11.21                                            1.83    ______________________________________     Abbreviations:     h  hour     1Br, etc = singly branched, etc.     D = Degree of Branching.

Table 2 below shows the mole fraction of the various isomers of nonenein the feed and the product over various time periods.

                  TABLE 2    ______________________________________                         0.6 to    Isomers      FEED    1.1 h   2.2 to 2.6 h                                         4.3 to 4.7 h    ______________________________________    2,2,5 Tri Me Hexane                 1.19    2.82    3.18    2.97    2,2,4 Tri Me Hexane                 0.75    0.48    0.52    0.82    2,3,5 Tri Me Hexane                 3.71    4.50    4.20    4.34    2,2 Di Me Heptane                 1.74    1.46    1.66    1.72    2,4 Di Me Heptane                 10.04   9.46    8.99    9.44    2 Me 4 Et Hexane                 3.48    2.87    3.14    3.04    2,6 Di Me Heptane                 3.89    5.50    5.65    5.47    2,5 Di Me Heptane                 21.23   22.56   22.87   22.73    3,5 Di Me Heptane                 0.00    1.44    0.00    1.02    2,4 Di Me 3 Et Pentane                 2.85    1.13    1.64    0.99    2,3,3 Tri Me Hexane                 1.07    0.28    0.88    0.36    2 Me 3 Et Hexane                 4.32    2.05    2.10    1.91    2,3,4 Tri Me Hexane                 2.43    0.96    1.14    0.98    3,3,4 Tri Me Hexane                 2.02    0.69    1.22    0.76    2,3 Di Me Heptane                 13.50   7.80    6.65    7.28    3,4 Di Me Heptane                 17.77   9.45    8.28    8.26    4 Me Octane  2.70    8.30    8.15    9.09    2 Me Octane  1.66    6.45    6.28    5.97    3 Et Heptane 1.01    2.01    2.44    1.95    3 Me Octane  3.45    9.78    9.70    10.21    n Nonane     1.22    0.00    1.30    0.68    ______________________________________

Table 3 shows the proportions, in weight percent, of species of variouscarbon number ranges in the feed and the product over various timeperiods, as determined by gas chromatography.

                  TABLE 3    ______________________________________    Feed        0.6 to 1.1 h                           1.7 to 2.2 h                                      4.3 to 4.7 h    ______________________________________    up to C.sub.8            0.8     2.3        1.5      1.2    C.sub.9 and C.sub.10            97.6    84.0       89.9     93.8    greater than            1.6     --         --       --    C.sub.10    C.sub.11 to C.sub.16            --      6.2        4.5      1.7    C.sub.18            --      7.5        5.3      3.3    ______________________________________

The results in Tables 1 to 3 above indicate a decrease in the degree ofbranching of the nonenes, primarily from a decrease in di-branching andan increase in single branching, accompanied by a decrease in 2,3-and3,4-dimethyl heptenes and an increase in 2,5- and 2,6-isomers. Nosignificant deactivation of the catalyst was observed over the durationor the test.

EXAMPLE 2

In this example, an undiluted nonene was used in a batch process. Thereaction conditions were as follows:

    ______________________________________    Feed         100% nonene fraction, composition as in                 Example 1.    Catalyst     H-ZSM 22, 10% by weight of feed.    Temperature  200° C.    Pressure     300 kPa    Phase        Liquid    Reactor      Stirred autoclave    Duration     9.5 hours.    ______________________________________

Table 4 shows the composition, in terms of branching of the nonenefraction, of the feed and the reaction mixture as sampled at the timesshown.

                  TABLE 4    ______________________________________    ISOMERS, %    LINEAR         1-Br   2-Br      3-Br D    ______________________________________    FEED    0.9        6.0    86.3    6.6  1.98    Product    1.5 h   0.8        10.5   81.9    6.8  1.95    3.5 h   2.0        19.2   71.8    7.0  1.84    9.5 h   1.4        26.9   63.9    7.8  1.78    ______________________________________

Table 5 shows the mole fraction of isomers of di-branched nonenes aftervarious times .

                  TABLE 5    ______________________________________               FEED  1.5 h      3.5 h  9.5 h    ______________________________________    26           3.7     7.9        10.0 13.3    25 + 35      30.8    31.7       35.6 40.1    24           13.5    13.1       13.3 13.7    23 + 3E3M    16.8    15.6       14.1 11.8    22           1.6     2.0        2.1  2.2    2M3E + 234)* 10.5    9.5        8.3  5.7    34 + 4E      22.7    19.9       16.9 13.3    ______________________________________     *No separation of GC peaks obtained.     Abbreviations:     26,etc = 2,6dimethylheptenes, etc     3E3M, etc = 3ethyl-3-methylhexenes, etc     234 = 2,3,4trimethylhexenes.

The results in Tables 4 and 5 show that after 9.5 hours the productdistribution, as indicated by the nonene isomers, is very similar tothat of Example 1, as shown in Tables 1 and 2.

EXAMPLE 3

The reaction was carried out in an autoclave under autogenous pressure,with the temperature being maintained at 165° C., for 24 hours. The feedwas 50 g of an isomeric mixture of heptenes, the catalyst was 10 g ofH-ZSM-22 powder.

Table 6 shows the composition of the feed and the final product.

                  TABLE 6    ______________________________________                     FEED  PRODUCT    ______________________________________    Heptene Isomers    2,2 Di Me Pentane  2.28    0.53    2,4 Di Me Pentane  18.20   14.63    2,2,3 Tri Me Pentane                       0.59    2.03    3,3 Di Me Pentane  0.33    0.00    2 Me Hexane        15.05   29.55    2,3 Di Me Pentane  36.06   29.47    3 Me Hexane        21.79   18.86    3 Et Pentane       2.62    1.41    n Heptane          3.08    3.52    Heptene isomer distribution    Linear             3.08    3.52    Mono-branched      39.47   49.82    Di-branched        56.86   44.63    Tri-branched       0.59    2.03    D                  1.55    1.45    ______________________________________

EXAMPLE 4

In this example, carried out like Example 3 in an autoclave atautogenous pressure, the feed was a mixture of octene and nonene isomerswith the octenes forming the major fraction. 10% by weight, based on theweight of feed, of H-ZSM-22-catalyst was employed, and the temperaturemaintained at 190° C., for 24 hours. The results are shown in Tables 7and 8.

                  TABLE 7    ______________________________________                     FEED  PRODUCT    ______________________________________    Octene Isomers    2,2,4 Tri Me Pentane                       0.14    0.00    2,2 Di Me Hexane   3.77    5.33    2,5 Di Me Hexane   12.84   12.98    2,4 Di Me Hexane   18.07   18.61    2,2,3 Tri Me Pentane                       3.21    3.45    3,3 Di Me Hexane   3.43    2.30    2,3,4 Tri Me Pentane                       8.36    8.99    2,3,3 Tri Me Pentane                       1.37    1.34    2,3 Di Me Hexane   18.93   14.76    2 Me 3 Et Pentane  0.00    0.00    2 Me Heptane       5.04    6.89    4 Me Heptane       3.95    3.64    3,4 Di Me Hexane   10.85   9.99    3 Me Heptane       7.20    10.27    n Octane           2.85    1.45    Octene Isomer Distribution    Linear             2.85    1.45    Mono-branched      16.18   20.80    Di-branched        67.88   63.97    Tri-branched       13.09   13.78    D                  1.91    1.90    ______________________________________

                  TABLE 8    ______________________________________                     FEED  PRODUCT    ______________________________________    Nonene Isomers    2,2,5 Tri Me Hexane                       13.54   14.95    2,2,4 Tri Me Hexane                       9.08    3.49    2,3,5 Tri Me Hexane                       10.85   14.47    2,2 Di Me Heptane  8.67    2.38    2,4 Di Me Heptane  12.83   9.22    2 Me 4 Et Hexane   4.67    4.61    2,6 Di Me Heptane  5.02    2.59    2,5 Di Me Heptane  10.80   11.60    3,5 Di Me Heptane  0.00    4.05    2,4 Di Me 3 Et Pentane                       4.31    1.68    2,3,3 Tri Me Hexane                       2.08    0.28    2 Me 3 Et Hexane   3.04    2.45    2,3,4 Tri Me Hexane                       1.93    1.82    3,3,4 Tri Me Hexane                       1.22    1.33    2,3 Di Me Heptane  4.61    9.22    3,4 Di Me Heptane  4.06    7.90    4 Me Octane        1.52    2.38    2 Me Octane        0.00    2.03    3 Et Heptane       0.00    0.28    3 Me Octane        1.22    3.28    n Nonane           0.00    0.00    Nonene isomer distribution    Linear             0.00    0.00    Mono-branched      2.74    7.97    Di-branched        53.70   54.02    Tri-branched       43.56   38.02    D                  2.41    2.30    ______________________________________

EXAMPLE 5

Example 4 was repeated, but using 20% by weight of catalyst. The resultsare shown in Tables 9 and 10 below.

                  TABLE 9    ______________________________________                     FEED  PRODUCT    ______________________________________    Octene Isomers    2,2,4 Tri Me Pentane                       0.14    0.00    2,2 Di Me Hexane   3.77    1.90    2,5 Di Me Hexane   12.84   12.14    2,4 Di Me Hexane   18.07   18.38    2,2,3 Tri Me Pentane                       3.21    1.54    3,3 Di Me Hexane   3.43    1.07    2,3,4 Tri Me Pentane                       8.36    4.36    2,3,3 Tri Me Pentane                       1.37    0.75    2,3 Di Me Hexane   18.93   11.48    2 Me 3 Et Pentane  0.00    0.00    2 Me Heptane       5.04    12.89    4 Me Heptane       3.95    5.90    3,4 Di Me Heptane  10.85   6.28    3 Me Heptane       7.20    18.98    n Octane           2.85    4.33    Octene Isomer Distribution    Linear             2.85    4.33    Mono-branched      16.18   37.77    Di-branched        67.88   51.25    Tri-branched       13.09   6.65    D                  1.91    1.60    ______________________________________

                  TABLE 10    ______________________________________                     FEED  PRODUCT    ______________________________________    Nonene Isomers    2,2,5 Tri Me Hexane                       13.54   12.91    2,2,4 Tri Me Hexane                       9.08    4.91    2,3,5 Tri Me Hexane                       10.85   12.30    2,2 Di Me Heptane  8.67    1.67    2,4 Di Me Heptane  12.83   7.44    2 Me 4 Et Hexane   4.67    2.94    2,6 Di Me Heptane  5.02    4.71    2,5 Di Me Heptane  10.80   16.61    3,5 Di Me Heptane  0.00    0.00    2,4 Di Me 3 Et Pentane                       4.31    1.87    2,3,3 Tri Me Hexane                       2.08    0.00    2 Me 3 Et Hexane   3.04    1.16    2,3,4 Tri Me Hexane                       1.93    2.03    3,3,4 Tri Me Hexane                       1.77    1.57    2,3 Di Me Heptane  4.61    5.06    3,4 Di Me Heptane  4.06    5.52    4 Me Octane        1.52    5.42    2 Me Octane        0.00    5.06    3 Et Heptane       0.00    1.47    3 Me Octane        1.22    7.34    n Nonane           0.00    0.00    Nonene isomer distribution    Linear             0.00    0.00    Mono-branched      2.74    19.29    Di-branched        53.70   45.11    Tri-branched       43.56   35.59    D                  2.41    2.16    ______________________________________

EXAMPLE 6

Example 4 was repeated, but using as feed an octene mixture obtained bythe dimerization of isobutylene; the temperature was maintained at 200°C. The results are shown in Tables 11 and 12 below.

                  TABLE 11    ______________________________________                  FEED  PPODUCT    ______________________________________    Linear          0.0     0.82    Mono-branched   0.0     17.58    Di-brancbed     0.48    25.04    Tri-branched    99.52   56.55    D               3.00    2.37    ______________________________________

                  TABLE 12    ______________________________________    Octene Isomers   FEED    PRODUCT    ______________________________________    2,2,4 Tri Me Pentane                     96.14   9.70    2,2 Di Me Hexane 0.48    0.99    2,5 Di Me Hexane 0.00    5.05    2,4 Di Me Hexane 0.00    8.43    2,2,3 Tri Me Pentane                     1.71    9.33    3,3 Di Me Hexane 0.00    1.49    2,3,4 Tri Me Pentane                     1.16    33.13    2,3,3 Tri Me Pentane                     0.51    4.40    2,3 Di Me Hexane 0.00    5.99    2 Me 3 Et Pentane                     0.00    0.00    2 Me Heptane     0.00    5.70    4 Me Heptane     0.00    2.98    3,4 Di Me Hexane 0.00    3.08    3 Me Heptane     0.00    8.90    n Octane         0.00    0.82    ______________________________________

EXAMPLE 7

Example 4 was repeated, but using a nonene feed. The results are shownin Table 13.

                  TABLE 13    ______________________________________                     FEED  PRODUCT    ______________________________________    Nonene isomers    2,2,5 Tri Me Hexane                       1.19    3.26    2,2,4 Tri Me Hexane                       0.75    1.26    2,3,5 Tri Me Hexane                       3.71    4.80    2,2 Di Me Heptane  1.74    1.82    2,4 Di Me Heptane  10.04   8.41    2 Me 4 Et Hexane   3.48    3.59    2,6 Di Me Heptane  3.89    5.46    2,5 Di Me Heptane  21.23   21.65    3,5 Di Me Heptane  0.00    0.00    2,4 Di Me 3 Et Pentane                       2.85    1.38    2,3,3 Tri Me Hexane                       1.07    0.86    2 Me 3 Et Hexane   4.32    2.12    2,3,4 Tri Me Hexane                       2.43    1.72    3,3,4 Tri Me Hexane                       2.02    1.42    2,3 Di Me Heptane  13.50   7.69    3,4 Di Me Heptane  17.77   8.25    4 Me Octane        2.70    8.12    2 Me Octane        1.66    6.23    3 Et Heptane       1.01    2.12    3 Me Octane        3.45    9.85    n Nonane           1.22    0.00    Nonene isomer distribution    Linear             1.22    0.00    Mono-branched      8.81    26.32    Di-branched        75.96   58.98    Tri-branched       14.01   14.70    D                  2.03    1.88    ______________________________________

EXAMPLE 8

In this example, the catalyst was H-ZSM-22 in 3 mm extrudate form usedat 10 % by weight of a nonene feed. The isomerization reaction wascarried out for 24 hours at 200° C. in an autoclave under autogenouspressure. The results are shown in Table 14.

                  TABLE 14    ______________________________________                     FEED  PRODUCT    ______________________________________    Nonene isomer distribution    Linear             1.22    1.49    Mono-branched      8.81    20.50    Di-branched        75.96   65.23    Tri-branched       14.01   12.78    D                  2.03    1.89    Nonene isomers    2,2,5 Tri Me Hexane                       1.19    2.46    2,2,4 Tri Me Hexane                       0.75    1.01    2,3,5 Tri Me Hexane                       3.71    4.05    2,2 Di Me Heptane  1.74    1.48    2,4 Di Me Heptane  10.04   8.48    2 Me 4 Et Hexane   3.48    3.90    2,6 Di Me Heptane  3.89    4.45    2,5 Di Me Heptane  21.23   17.77    3,5 Di Me Heptane  0.00    4.77    2,4 Di Me 3 Et Pentane                       2.85    1.77    2,3,3 Tri Me Hexane                       1.07    0.34    2 Me 3 Et Hexane   4.32    2.67    2,3,4 Tri Me Hexane                       2.43    1.82    3,3,4 Tri Me Hexane                       2.02    1.33    2,3 Di Me Heptane  13.50   10.19    3,4 Di Me Heptane  17.77   11.51    4 Me Octane        2.70    5.62    2 Me Octane        1.66    5.69    3 Et Heptane       1.01    1.37    3 Me Octane        3.45    7.83    n Nonane           1.22    1.49    ______________________________________

EXAMPLE 9

Example 8 was repeated, but isomerization was carried out for 6 hoursonly. The results are shown in Table 15.

                  TABLE 15    ______________________________________                     FEED  PRODUCT    ______________________________________    Nonene isomers    2,2,5 Tri Me Hexane                       1.19    1.79    2,2,4 Tri Me Hexane                       0.75    0.84    2,3,5 Tri Me Hexane                       3.71    4.00    2,2 Di Me Heptane  1.74    1.72    2,4 Di Me Heptane  10.04   8.53    2 Me 4 Et Hexane   3.48    3.62    2,6 Di Me Heptane  3.89    3.61    2,5 Di Me Heptane  21.23   17.13    3,5 Di Me Heptane  0.00    4.23    2,4 Di Me 3 Et Pentane                       2.85    2.39    2,3,3 Tri Me Hexane                       1.07    0.28    2 Me 3 Et Hexane   4.32    3.51    2,3,4 Tri Me Hexane                       2.43    2.04    3,3,4 Tri Me Hexane                       2.02    1.47    2,3 Di Me Heptane  13.50   11.97    3,4 Di Me Heptane  17.77   14.54    4 Me Octane        2.70    4.81    2 Me Octane        1.66    4.25    3 Et Heptane       1.01    0.95    3 Me Octane        3.45    7.01    n Nonane           1.22    1.30    Nonene isomer distribution    Linear             1.22    1.30    Mono-branched      8.81    17.02    Di-branched        75.96   68.86    Tri-branched       14.01   12.82    D                  2.03    1.93    ______________________________________

A comparison of Examples 8 and 9 shows that prolonging the isomerizationreaction produces a lower degree of branching. This is, however, at theexpense of decreasing yield, because of the competing oligomerizationreaction.

We claim:
 1. A method of isomerizing a branched olefinic feedstock containing at least one olefin having a carbon number within the range of from 4 to 20, which comprises contacting the feedstock under conditions favoring skeletal isomerization with a zeolite free of added catalytic metal selected from the group consisting of ZSM-22, ZSM-23 and ZSM-48 at a temperature in the range of 50° to 350° C., the product of said isomerization having a reduced average degree of branching as compared with said olefin feedstock.
 2. The method of claim 1, wherein the feedstock contains at least one olefin having a carbon number within the range of from 7 to
 16. 3. The method of claim 1, wherein the feedstock contains at least one alkene with from 7 to 12 carbon atoms.
 4. The method of claim 1, wherein the feedstock is a mixture of isomers having the same number of carbon atoms.
 5. The method of claim 1, wherein the feedstock is a mixture of olefins having a range of carbon atom numbers.
 6. The method of claim 1, wherein the feedstock comprises nonenes.
 7. The method of claim 6 wherein the feedstock has a degree of branching in excess of 1.95.
 8. The method of claim 1, wherein the zeolite is ZSM-22.
 9. The method of claim 1, wherein the zeolite is in the acidic form.
 10. The method of claim 1, wherein the zeolite has been calcined.
 11. The method of claim 1, wherein the zeolite is in powder, granule or extrudate form.
 12. The method of claim 1, carried out at a pressure between atmospheric pressure and 10 MPa.
 13. The method of claim 1, wherein the feedstock consists essentially of the branched olefin.
 14. The method of claim 1, wherein the feedstock comprises the branched olefin in admixture with a diluent or solvent.
 15. The method of claim 1 wherein said temperature is in the range of 150° to 250° C.
 16. A method of isomerizing a branched olefinic feedstock containing at least one olefin having a carbon number within the range of from 4 to 20, which comprises contacting the feedstock under conditions favoring skeletal isomerization with a acidic zeolite free of added catalytic metal having a ten membered ring pore structure at a temperature in the range of 50° to 350° C., the product of said isomerization having a reduced average degree of branching as compared with said olefin feedstock.
 17. The process of claim 16 wherein said zeolite is ZSM-22. 